Cumene and Cumene Production
Cumene is an aromatic compound. It is a clear liquid at ambient conditions. High purity cumene is conventionally manufactured from propylene and benzene. Cumene is used today primarily as a feed in manufacturing the products phenol and acetone, which are two important petrochemicals with many uses in the chemical and polymer industries. Global cumene production in 1998 was about 7 million metric tons.
Cumene was first synthesized in large quantities during World War II as an aviation gasoline. It has a high heating value and a high octane number, but it is not economically competitive today as a fuel. Its presence in gasoline is now incidental, being an inevitable minor reaction product of refinery processes such as catalytic reforming and steam cracking.
Production of cumene was considered a rather conventional and routine business for many years, but recently has generated considerable excitement for two reasons. First, the demand for phenol for manufacturing polycarbonates is accelerating rapidly owing to the broadening applications of polycarbonates in the electronic, healthcare, and automobile industries. Second, successful development and commercialization of the zeolite-based alkylation technology for the isopropylation of benzene to cumene has rendered obsolete the older processes which were based on solid phosphoric acid and aluminum chloride. Within a period of just over two years during 1996-98, over one half of the cumene capacity in the world was converted to the new zeolite technologies.
New zeolite-based cumene technologies developed by Mobil/Badger, Dow/Kellogg, and UOP carry out the alkylation of benzene and propylene in liquid phase in the presence of a solid acidic zeolite catalyst. A process developed by CDTech achieves the alkylation of benzene and propylene in mixed phases in a catalytic distillation column packed with both distillation devices and bales of zeolite catalysts. FIG. 1 is a simplified representation of the zeolite-based cumene technologies. All of these zeolite-based cumene technologies utilize a separate transalkylation zone which is operated in parallel with the alkylation zone, to react a mixture of benzene and the polyisopropylbenzene alkylation byproducts to form additional cumene in liquid phase in the presence of a solid acidic catalyst. A separation zone is utilized to recover the unreacted benzene and polyisopropylbenzenes for recycle, and to isolate the desired cumene product.
Ethylbenzene and Ethylbenzene Production
Ethylbenzene is a commodity chemical currently used mostly for the production of styrene. Global ethylbenzene production in 1998 was about 19 million metric tons. Ethyl-benzene may be prepared by a number of different chemical processes, but present commercial ethylbenzene production is dominated by zeolite-based technologies. The first zeolite-based ethylbenzene process, developed jointly by Mobil and Badger in the early 1980s, utilizes a combination of vapor phase alkylation of benzene with ethylene and vapor phase transalkylation of a benzene and polyethylbenzene mixture. Both the alkylation and transalkylation steps are carried out in the presence of solid acidic ZSM-5 catalysts.
Several liquid-phase zeolite-based ethylbenzene technologies were developed in the late 1980s and in the 1990s by UOP/Lummus and Mobil/Badger. Alkylation of benzene with ethylene and transalkylation of mixtures of benzene and polyethylbenzenes are carried out in liquid phase in the presence of solid acidic zeolite catalysts. Catalysts that can be used for alkylation of benzene with ethylene and for transalkylation of benzene and polyethylbenzenes in at least partial liquid phase include zeolite beta, zeolite Y, ZSM-5, PSH-3, ITQ-2, ZSM-12, MCM-22, MCM-36, MCM-49, MCM-56, MCM-58, MCM-68, faujasite, mordenite, porous crystalline magnesium silicates, and tungstate modified zirconia.
Processes for the production of ethylbenzene over intermediate-pore size zeolites are described in U.S. Pat. No. 3,751,504 (Keown), U.S. Pat. No. 4,547,605 (Kresge), and U.S. Pat. No. 4,016,218 (Haag). U.S. Pat. No. 4,169,111 (Wight) and U.S. Pat. No. 4,459,426 (Inwood) disclose production of ethylbenzene over large-pore size zeolites such as zeolite Y. A process for ethylbenzene production over zeolite ZSM-12 is described in U.S. Pat. No. 3,755,483 (Burress). Liquid phase synthesis of ethylbenzene with zeolite beta is described in U.S. Pat. No. 4,891,458.
To minimize the formation of polyalkylaromatics and other undesired impurities (e.g., oligomers of the olefin), production of alkylaromatics such as ethylbenzene and cumene typically operates with relatively high (excess) mole ratios of aromatic (e.g., benzene) to olefin (e.g., ethylene or propylene) in the alkylation reactor feed. Zeolite-based alkylaromatic processes generally operate at aromatic to olefin feed molar ratios of three or above, while aluminum chloride-based processes often operate at aromatic to olefin molar ratios of three and below. In both cases, however, the polyalkylaromatics are produced at sufficiently high levels that it would be prohibitively expensive to simply dispose of them as low value byproducts. Instead, these polyalkylated aromatics are typically reacted further with feed aromatic to form additional monoalkylate via transalkylation reactions.
In the case of the Mobil/Badger vapor phase ethylbenzene process mentioned above, the transalkylation reaction may take place in the alkylation reactor or in a separate transalkylation reactor. U.S. Pat. No. 5,902,917 (Collins) and U.S. Pat. No. 6,096,935 (Schulz) describe processes for the production of alkylaromatics wherein a feedstock is first fed to a transalkylation zone and the entire effluent from the transalkylation zone is then cascaded directly into an alkylation zone along with an olefin alkylating agent.
Conventionally, relatively high molar ratios of aromatic (e.g., benzene) to olefin (e.g., ethylene or propylene) have been used successfully commercially in the production of alkylaromatics (e.g., ethylbenzene or cumene) to minimize the formation of polyalkylaromatics and other undesired impurities (e.g., oligomers of the olefins). The disadvantage of using high molar ratios of aromatic to olefin, however, is that the recovery and the subsequent circulation (re-use) of the unreacted aromatics consumes very substantial amounts of energy which increases the production cost of the desired alkylaromatics.
The recovery and circulation of large amounts of unreacted aromatics also requires larger capacity separation equipment (usually distillation columns) and larger pumps, both of which increase capital cost of the plant, and thus also increase the cost of production.
It is therefore of crucial interest to minimize the amount of excess aromatics that is used and needs to be recovered and subsequently circulated in order to minimize the production cost. It is of even more importance today in the production of highly competitive commodity chemicals (e.g., ethylbenzene and cumene) which are produced and traded globally, and at a time when the energy costs are high. Low aromatics circulation results in lower energy consumption, lower capital investment and thus a more efficient plant. This in turn enables a producer to establish itself as a low cost producer in a favorable (competitive) marketing position.
Because of these disadvantages and limitations of the prior art processes, it is desired to provide improved processes and apparatus for the production of alkylaromatic compounds. In this invention, two reaction configurations are provided which have been found to significantly reduce the total aromatic circulation, compared with prior art processes, at all aromatic to olefin ratios.